Gonorrhea is a common bacterial infection that is transmitted primarily by sexual contact. Gonococcal infections have an epidemiological pattern characterized by the concentration of infections in social or geographically defined communities termed "core groups". These "core groups" have been proposed as reservoirs for the continued transmission of infections within communities, and therefore, understanding the biological nature of the constituent organisms is important for public health control strategies. We propose to examine the molecular evolution of Neisseria gonorrhea within a community over time and in relation to epidemiological information pertaining to the host individuals. This is a collaborative effort between two experts in infectious disease and epidemiology of gonorrhea and a population geneticist. Two molecular typing methods will be used to characterize gonococcal isolates: por gene sequencing and multi-locus sequence typing (MLST) scheme, in which alleles at six housekeeping genes are characterized by sequencing approximately 500 bp internal fragments of the genes. The study has three main objectives The first is to determine temporal trends in the population genetic structure of N. gonorrhea over a 20-year period in a high prevalence community, Baltimore, MD. The second is to correlate changes in population genetic parameters with epidemiological information pertaining to the host individual's residence in a "core" or "peripheral" region. Our major hypothesis is that higher levels of genetic diversity, more intense selection pressure on the por gene, a positive growth rate, and a higher recombination rate relative to the peripheral population will characterize the population genetic structure of N. gonorrhea in the core. The third aim is to determine whether gender, age, or disseminated versus local infection influences the population genetic structure of N. gonorrhea.